Allow file format to be upper/lowercase in save_results

[lforesta]

According to the openEO API spec: "Format names are allowed to be case insensitive throughout the API."

[soxofaan]

This actually raises the question why it states "are allowed to be case insensitive".
Does this mean that a backend can choose to be case insensitive about format names?
Wouldn't it be better (for portability) to enforce that format names are case insensitive?
(same for Service names and Billing plans by the way)

cc @m-mohr

[m-mohr]

A back-end must accept formats case-insensitive to make it easier for users to use. We had a number of workshops where people had issues with that, e.g. the back-end exposed "GTiff" and people just typed "gtiff" in the client. This is purely for a better user experience. Maybe we need to improve wording in the API, this is clearly written from a client perspective.

[m-mohr]

See PR Open-EO/openeo-api#372

[clausmichele]

This issue has been solved here #25